1. Field of the Invention
The present invention is directed to a machine for heat-sealing a patch to a plastic article and more specifically to a machine for perforating a plastic bag and heat-sealing a semipermeable membrane to the plastic bag to cover the perforation.
2. Prior Art
For many years flexible containers such as plastic bags have been provided with spouts or valves by means of a machine which will first punch an opening in the plastic bag from one side and heat-seal a spout to the plastic material from the opposite side. Furthermore, the apparatus for carrying out this dual function is extremely complicated and expensive due to the fact that the heat-sealing head, the pressure platen and the punching apparatus are all disposed coaxially with respect to each other.
The use of plastic packages having a semipervious membrane covering an opening therein to facilitate the sterilization of the products are old and well known in the art. Such packages are generally made of polyolefin plastic material such as polyethylene, polypropylene, copolymers or mixtures of polyethylene and polypropylene. Generally, a low density polyethylene is used for the package and a spun-bonded, non-woven polyethylene sheet member such as TYVEK, produced by Dupont Chemical Company, is used for the semipermeable patch or membrane. Some of the prior art packages of this nature merely close the two edges which define the mouth of the package by means of a strip of the semipermeable material which can be heat-sealed to the plastic bag. Another type of package of this nature forms a continuous cut or slit in the plastic sheet material as it passes from a supply roll and subsequently heat-seals the sheet material into the form of a bag and applies an elongated patch of the semipermeable material over the slit. The completed bags are then severed from the continuous sheet of material. Still other prior art bags provide a plurality of perforations in the plastic bag and cover them with a heat-sealing tape which is applied by a completely separate operation. In general, the construction of all of the prior art bags of this nature either involve a completely automated system wherein the plurality of steps are performed in sequence automatically during the formation of the bag which results in extremely high equipment cost or else the perforations and patches are performed subsequently by individual independent steps which involve a considerable amount of bag handling which is both inefficient and time consuming.